Use these commands to move the frame exactly where you want it:
Code:
/run ChatFrame1:ClearAllPoints()
/run ChatFrame1:SetPoint("BOTTOMLEFT", UIParent, 100, 25)
/run ChatFrame1:SetUserPlaced(true)
/run ChatFrame1:SetSize(600, 200)
In the SetPoint command, the first number is the horizontal offset from the specified point, and the second is the vertical. Positive numbers move left/up, while negative numbers move right/down. In the SetSize command, the first number is the width, and the second is the height.
Then invoke the default UI's own function to save the position and size so they'll be loaded again in the future:
Code:
/run FCF_SavePositionAndDimensions(ChatFrame1)
If you want to see the currently saved position and size for reference:
Code:
/dump GetChatWindowSavedPosition(ChatFrame1)
/dump GetChatWindowSavedDimensions(ChatFrame1)